A subject matter of the invention is a process for the treatment by an ion beam of a powder based on cerium oxide, in particular of a promoter based on cerium oxide, with the aim of increasing the mobility of the oxygen at the surface of and inside the promoter, of reducing the temperature for reduction of the promoter, of increasing the yield of the reactions with which the promoter is associated and of reducing the amount of catalyst, the catalytic power of which it promotes.
It should be remembered that, in catalysis, a promoter is a compound, generally provided in the powder form, which increases the catalytic power of a catalyst, without itself having an intrinsic catalytic power.
Promoter based on cerium oxide is understood to mean a promoter comprising at least one atom of cerium and of oxygen. This family of promoters is known for its ability to store and to release oxygen and is used in particular in motor vehicle mufflers. Promoters based on cerium oxide act as a reservoir of oxygen for oxidation/reduction reactions involving the Ce4+/Ce3+ pair. They make it possible, for example, to increase the three-way catalytic deposition effectiveness by widening the air/fuel adjustment window.
For some years, the problems related to the environment have been increasing in scale. One of the major problems is the atmospheric pollution caused by motor vehicles. In order to limit pollution by motor vehicles and in particular emissions of carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx), cars have been progressively equipped with catalytic converters. The role of the latter is to convert harmful pollutant molecules (CO, HC and NOx) into nontoxic entities (CO2, N2 and H2O): this is “three-way” catalysis. In recent years, ceria-zirconia solid solutions have appeared dominant in the formulations of three-way catalysts at the expense of ceria, as they exhibit a high oxygen storage capacity and furthermore withstand high-temperature treatments. However, the conditions of use of catalytic converters during startup of the engines under cold conditions make desirable, indeed even force, a further improvement in the redox efficiency of these oxides at low temperature. Recent studies on the Ce—Sn—O ternary system indicate that Ce2Sn2O7—Ce2Sn2O8 oxides of pyrochlore type also exhibit oxygen storage properties.
This results in a need for a method for the treatment of powders based on cerium oxide, in particular of promoters in the powder form based on cerium oxide, exhibiting an improved redox efficiency at low temperature, preferably according to methods which can be easily operated on the industrial scale, so as to be able to present such powders, in particular promoters, in a significant amount and at reasonable costs.